How can I link two database tables together

I'm not too sure how else to word this question, as I can't find anything on google about it.

Basically, I have a user and they create products. This is the schema:

  create_table "users", force: :cascade do |t|
    t.string   "email"
    t.string   "username"
    t.string   "encrypted_password"
    t.string   "description"
    t.string   "address"
    t.string   "phone_number"
 end

  create_table "products", force: :cascade do |t|
    t.string   "name",                default: "", null: false
    t.string   "description"
    t.string   "quantity"
    t.datetime "created_at",                       null: false
    t.datetime "updated_at",                       null: false
    t.integer  "user_id"
  end

What I want to do is something like this:

@products.users.username

So I can associate the user with a product they have created. My model is as followed:

class User < ActiveRecord::Base
  has_many :products
end

class Product < ActiveRecord::Base
  belongs_to :user
end

And for my product controller, namely for show.html.erb:

  def show
    @products = Product.find(params[:id])
  end

Basically, when you're on the show.html.erb page, you can click the product and it loads the product's information page, and I want the product information page to list the user who created the product. I thought something like this would work:

@products.user.username

However, it tells me "undefined username", and I have a feeling there is something I have missed. Currently, when a product is created, the product is associated with a user id.

Thank you for your help.